The lime represents a branching path you can take in a game.

There are points in a game that are impossible to return to after leaving the area or like killing a certain boss enemy.

When there are cool/special items hidden in those areas, if you leave and can’t come back you might miss the item and never get to use it unless you restart and play the game all over again just to get the chance to pick it up again.

Things get much worse when there are multiple items or even boss fights like this in the same game, where doing things ouf of order can lock you out of full questlines (like in Elden Ring where reaching Altus Plateau before getting as far as possible through everyone’s questlines will make half of them unable to be completed for no reason whatsoever)